Axial piston type variable displacement fluid motor/pump units have been in existence for many years. However, they have been confined to rather limited application because of one or more design limitations. The prior art axial piston variable displacement fluid motor/pump units have generally been limited by one or more of the following design limitations: inefficiency of operation at low speeds particularly below 500 revolutions per minute; the generation of unacceptable levels of noise; highly susceptable to particle contamination in the fluid; inability to operate efficiently at high speeds; inability to operate efficiently over a very wide range of speeds; large axial forces requiring the use of expensive or multiple thrust bearings; the high weight to pumping displacement ratio; the substantial cost with respect to the amount of pumping displacement; the inordinant amount of rotating mass requiring large bearings and shafts; and limited operational life before major repairs are required.
Small particles in the neighborhood of 10 to 20 microns have been known to cause premature mechanical failures because of the excessively large mechanical loads between the traditional piston shoe, wear plate, valve ports and wear plate interfaces.
The principal objective of the present application is to overcome many, if not all, of the previous design limitations. A further objective is to provide such a unit that can operate efficiently over a wide range of speeds.
The present invention provides for higher efficiencies of the apparatus over a wider range of speeds including continuously variable speeds at any desired flow rate with a substantial increase in operation between maintenance periods. Furthermore, the present invention provides a system for equalizing forces within the unit to reduce the numbers and size of bearings and shafts which in turn substantially reduces the weight to displacement ratio. Additionally, the present invention greatly increases the variety of applications and alternative modes of operation from a single mechanical device.
These and other objects and advantages of this invention will become apparent upon reading the following detailed description of a preferred embodiment.